The present invention relates to an automatic two-sided recording apparatus capable of recording images on both sides of a recording sheet of a sheet type, and particularly to an automatic two-sided recording apparatus capable of processing automatic two-sided recording at high speed.
In the field of image recording apparatuses such as an electrophotographic copying machine and a laser printer, there have been proposed various technologies of an automatic two-sided recording apparatus capable of recording not only on one side but also on both sides of a recording sheet. In a conventional automatic two-sided recording apparatus, an image is recorded on one side of a sheet at an image processing section, then the sheet is stored temporarily in an intermediate stacker (intermediate tray), and the sheet is conveyed again to an image forming section. An automatic sheet circulation-conveying apparatus of this type is disclosed in Japanese Patent O.P.I. Publication Nos. 82247/1984 and 114227/1984.
In the case of a two-sided copy mode for a single sheet, the recording sheet is subjected to one-sided copying, then the recording sheet is ejected out of an apparatus temporarily by an ejection roller to be turned upside down, and is fed to the image forming section again through the aforesaid circulation-conveying path so that copy images are formed on the opposite side of the recording sheet. In the case of two-sided copying for plural sheets, on the other hand, a recording sheet whose one side has been recorded is fed to the image forming section again through the intermediate stacker so that copy images are formed on the opposite side of the recording sheet. With regard to the two-sided copying apparatus that circulation-conveys a single recording sheet and plural recording sheets, Japanese Patent O.P.I. Publication Nos. 111955/1983 and 183471/1987 are known.
The aforementioned publications disclose that a conveyance path which does not pass through an intermediate stacker and a conveyance path which passes through the intermediate stacker are provided for recording on the other side of a sheet whose one side has been recorded, and recording sheets are stacked on the intermediate stacker temporarily and then are conveyed when a plurality of copies are needed. In the aforementioned conventional copying machine, there have been caused disadvantages mentioned below because a sheet conveyance path used for feeding again the sheet stacked temporarily in the intermediate stacker and a sheet conveyance path used for feeding again the sheet directly without stacking are separated independently.
Namely, it is unavoidable that the two-sided copying apparatus is complicated in structure, resulting in production cost increase. Further, switching operations are complicated, which causes occurrence of troubles. Operations of timing in the course of sheet conveyance are also complicated and adjustment therefor is difficult. Therefore, it is unavoidable that reliability of the total apparatus is lowered.
The applicant of the invention have applied U.S. Pat. No. 5,331,386 (Jul. 19, 1994) wherein the disadvantages have been solved and circulation conveyance of recording sheets, conveyance efficiency and a speed of copy processing are improved. The recording sheet conveyance device in the aforementioned publication is represented by a recording sheet conveyance device of a two-sided recording type stacking a recording sheet fed from a sheet supply section in an intermediate tray of the recording sheet conveyance device after image recording on one side of the recording sheet by an image forming section, and conveying further the recording sheet so that images may be recorded on the other side of the recording sheet in the aforementioned image forming section, wherein a sheet-feeding/ejecting means capable of rotating forwardly and reversely for ejecting or feeding the recording sheet to the intermediate tray is provided for the purpose of recording on the other side of the recording sheet whose one side has been recorded, and a recording sheet conveyance path is used in common for both an established stackless mode in which the recording sheet is fed by the aforementioned sheet-feeding/ejecting means again one by one being held by its one end without being stacked in the intermediate tray and an established stack mode in which the recording sheet is stacked in the intermediate tray and then is fed again.
The problem of a conventional copying apparatus is that an interval from copying on the obverse side to copying on the reverse side is extremely long. The reason for this is that copying on the reverse side is started after all the recording sheet are stacked temporarily on an intermediate tray. This problem has been solved in the aforementioned U.S. Pat. No. 5,331,386, and there has been made a proposal for conveying recording sheets wherein a control means including constant A of a master table established in advance based on various conditions of sizes of recording sheets and/or copying magnifications is provided, and conveyance of the recording sheet is conducted by selecting a stackless mode or a stack mode by means of comparison control between the aforementioned sizes of the recording sheets and/or signals of processing sheet quantity and the constant A. However, the above-mentioned master table used in selection of a stackless mode or a stack mode becomes complicated when the copying magnification is one such as a zoom magnification, resulting in fall of reliability. In addition, operations of an optical system and conveyance of recording sheets are varied depending on differences between apparatuses, deterioration with the passage of time and environmental conditions, and reliability is further lowered.